Density functional study on the pressure profile of the inhomogeneous fluid mixture

By using the statistical mechanics, the pressure tensor for the multi component fluid mixture is derived. With the help of the classical density functional theory, profiles of the pressure components are calculated, and the influence of the total volume fraction, ratio of volume fraction, and size asymmetry on the pressure are studied. In addition, our results show that for the mixture confined in the hard cavity, the pressure shows a discontinuity near the cavity wall. However, in the soft cavity condition, the discontinuity disappears.

High temperature and high pressure rheological properties of high-density water-based drilling fluids for deep wells

To maintain tight control over rheological properties of high-density water-based drilling fluids, it is essential to understand the factors influencing the theology of water-based drilling fluids. This paper examines temperature effects on the rheological properties of two types of high-density water-based drilling fluids （fresh water-based and brine-based） under high temperature and high pressure （HTHP） with a Fann 50SL rheometer. On the basis of the water-based drilling fluid systems formulated in laboratory, this paper mainly describes the influences of different types and concentration of clay, the content of a colloid stabilizer named GHJ-1 and fluid density on the rheological parameters such as viscosity and shear stress. In addition, the effects of aging temperature and aging time of the drilling fluid on these parameters were also examined. Clay content and proportions for different densities of brine-based fluids were recommended to effectively regulate the rheological properties. Four theological models, the Bingham, power law, Casson and H-B models, were employed to fit the rheological parameters. It turns out that the H-B model was the best one to describe the rheological properties of the high-density drilling fluid under HTHP conditions and power law model produced the worst fit. In addition, a new mathematical model that describes the apparent viscosity as a function of temperature and pressure was established and has been applied on site.

The association of cerebrospinal fluid pressure with optic nerve head and macular vessel density

The present study aims to investigate the effect of temporary cerebrospinal fluid pressure(CSFP) reduction on optic nerve head(ONH) and macular vessel density(VD) using optical coherence tomography angiography.Forty-four eyes of 44 adults with diagnostic lumbar puncture and CSFP reduction were recruited.Thirty-two eyes of 32 healthy volunteers were controls.ONH and macular VD images were evaluated differences between baseline and after CSFP reduction.The results showed that the mean CSFP decreased from(11.6±2.1) mm Hg to(8.2±3.4) mm Hg(P<0.001).VD in the macular regions decreased significantly after CSFP reduction in the study group(all P<0.05).The control group showed no significant changes in macular VD(all P>0.05).In the study group,decreased VD in the macular parainferior region was associated with CSFP reduction(R^(2)=0.192,P=0.003),the reduction of macular VD in parafoveal(R^(2)=0.098,P=0.018),parainferior(R^(2)=0.104,P=0.021),parasuperior(R^(2)=0.059,P=0.058),paranasal(R^(2)=0.057,P=0.042),paratemporal(R^(2)=0.079,P=0.026) was associated with mean ocular perfusion pressure decrease following CSFP reduction.ONH vessel density did not differ after CSFP reduction(all P>0.05).In conclusion,macular vessel density decreased in association with CSFP reduction.Retinal vessel density in the macular region is more sensitive than that in peripapillary region after CSFP reduction.

Computation of compressible flows with high density ratio and pressure ratio

The WENO method, RKDG method, RKDG method with original ghost fluid method, and RKDG method with modified ghost fluid method are applied to singlemedium and two-medium air-air, air-liquid compressible flows with high density and pressure ratios： We also provide a numerical comparison and analysis for the above methods. Numerical results show that, compared with the other methods, the RKDG method with modified ghost fluid method can obtain high resolution results and the correct position of the shock, and the computed solutions are converged to the physical solutions as themesh is refined.

NUMERICAL COMPUTATION OF PRESSURE GRADIENT FOR THE FLOW OF POWER-LAW FLUID IN ANNULUS WITH INNER CYLINDER EXECUTING A PLANETARY MOTION

With the governing equations for the flow of the power-law fluid in annulus with the inner cylinder executing a planetary motion being transformed by using the undetermined coefficient method, the formula of pressure gradient for this flow under the given flow rate and the relevant numerical calculation method are given in this article. Through the experiments on the flow of Hydrolyzed Polyacrylamide （HPAM） aqueous solution which can be regarded as a power-law fluid, the calculated results of the pressure gradient values are compared with measured data, the mean relative error between them is smaller than 5%, which verifies the results presented in this article.

CPA方程计算醇、水的比热容性质

针对立方型附加缔合项(CPA)状态方程(EoS)对比热容的计算精度不高的问题,采用11种包含不同性质的参数计算方法研究了CPA方程对极性缔合流体甲醇、乙醇、水比热容的计算精度。计算结果表明:不考虑比热容时,CPA方程的参数计算必须考虑蒸汽压性质,且蒸汽压计算精度越高,方程对液相比热容的预测精度越高;在参数计算中加入比热容后,CPA方程无法同时准确描述所有比热容性质,其中对液相比定压热容的计算精度最高;在参数计算过程中比热容性质只考虑液相比定压热容时,方程对蒸汽压、各相密度及液相比定压热容的平均绝对相对偏差都在3%及以内。

高温深井温压耦合下流体性质对井筒压力的影响特性

深井高温高压环境对流体密度和流体流变参数影响较大,忽略其作用使得井筒压力认识不准确,制约着钻完井作业安全。基于能量守恒原理,建立了井筒温度计算模型,考虑流体流态对温度压力影响,建立了温压耦合条件下井筒压力计算方法,结合现场实测数据验证了温度压力模型计算可靠性。研究表明:温度对流体密度和流变参数影响程度大于压力,随着井深增加,环空流体密度和动切力逐渐增大。随着循环时间增加,井底温度逐渐降低,环空流体密度、动切力及流性指数逐渐增大,而稠度系数逐渐降低;温压耦合条件下环空ECD低于未考虑工况,两者相差0.067 g/cm3。因此,若不考虑耦合对流体密度和流变参数影响时,使得设计流体密度偏低,易诱发溢流或井喷事故发生。该研究成果与认识为深层超深井井筒温度压力精细评价奠定了关键理论基础,降低了钻完井井下作业风险。

抗高温低密度水泥浆体系研究与应用

为解决低密度水泥浆高温强度低、减轻材料承压能力不高、低密度水泥浆配浆困难等难题,研制了低密度增强材料DRA-2S、优选了耐压105 MPa的高性能空心玻璃微珠、聚羧酸分散剂DRS-2S及其他配套抗高温水泥外加剂,开发了抗高温低密度固井水泥浆体系。研究结果表明,该水泥浆能够满足循环温度150℃、井底静止温度180℃、耐压105 MPa的固井要求,顶部127℃静胶凝13.3 h起强度,24 h抗压强度12.4 MPa。开发的抗高温低密度水泥浆在西南油气田高温探井ZJ2井Ф127 mm尾管固井成功应用,固井质量合格率96.7%,为西南油气田高温易漏失复杂深井勘探开发提供了固井技术支撑。

低流阻全外压平衡型膨胀节压降仿真计算

蒸汽管道温度高、敷设距离长,常采用补偿器补偿管道的热膨胀量。本文针对旁通直管压力平衡型膨胀节在压降上的不足,提出了一种DN500低流阻全外压平衡型膨胀节,采用Fluent软件对其压降进行计算,分析流体流通面积比和流体流向转变角度对其压降的影响。结果表明,当流体流通面积比为2.35,流体流向转变角度为25°~40°时,减阻效果最佳,且优于旋转补偿单元。根据仿真数据,拟合得到DN500低流阻全外压平衡型膨胀节的压降计算公式,能够快速进行压降计算,为实际工程应用提供理论依据。

一种井筒液面位置准确识别与分析方法

传统通过深度-压力关系图确定井筒液面位置的方法,当遇到压力不稳定、流体密度不均匀、测点少等情况时存在精度不够或无法计算的问题。提出了依靠试井手段,在测取全井筒多点压力、温度的基础上,先根据全部井段压力温度梯度判断液面所在井段,再利用液面上下的实测点的压力和压力梯度计算液面位置的补充算法。当上部的气柱只有一个测点或者根本没有测点而无法进行线性回归的情况下,传统算法无法计算液面的位置,因液面附近的流体性质与液面上下实测点的流体性质最为接近,此方法提高了液面计算的准确度。经SQ储气库S4-1等多口井成功应用,计算结果符合生产实际情况。该方法提高了井筒内流体密度不均匀条件下液面位置的计算精度,是传统液面位置计算的有效补充。

控压放水技术在超高压超强蠕变软泥岩钻井中的应用

针对库车山前钻井液密度不能均衡上部超高压超强变软泥岩地层和下部薄弱砂岩的矛盾,采用控压放水技术,降低钻井液密度,解决了软泥岩蠕变、溢流和漏失之间的矛盾。结果表明:采用排混浆回收的最低钻井液密度计算地层压力较为真实,可有效避免地层压力降低的假象;对于超高压强蠕变软泥岩地层,通过控压放水,钻井液密度由2.65g/cm降低至2.52g/cm,出水量控制在0.2~0.6m/h,满足了地层出水量的处理要求,保障了安全钻进;控压放水后下探验证软泥岩蠕变时,应先下探到软泥岩顶部,开泵循环,待振动筛无掉块返出后再进行下探,防止掉块影响判断软泥岩地层蠕变。超高压超强蠕变软泥岩控压放水技术拓宽了控压放水技术的运用范畴,对类似软泥岩安全钻进具有一定的参考性。

Calculation of safe drilling mud density window for shale formation by considering chemo-poro-mechanical coupling effect

It is difficult to define safe drilling mud density window for shale sections.To solve this problem,the general Biot effective stress principle developed by Heidug and Wong was modified.The Weibull statistical model was used to characterize the hydration strainrelated strength damage.Considering drilling fluid sealing barrier on shale,a calculation method of safe drilling mud density has been established for shale formation under drilling fluid sealing-inhibition-reverse osmosis effect,combined with a flow-diffusion coupling model.The influence of drilling fluid sealing and inhibiting parameters on safe drilling mud density window was analyzed.The study shows that enhancing drilling fluid sealing performance can reduce the pore pressure transmission and solute diffusion;the inhibiting performance of drilling fluid,especially inhibition to strength damage,is crucial for the wellbore collapse pressure of shale section with significant hydration property.The improvement of drilling fluid sealing and inhibition performance can lower collapse pressure and enhance fracturing pressure,and thus making the safe drilling fluid density window wider and the collapse period of wellbore longer.If there is osmosis flow in shale,induced osmosis flow can make the gap between collapse pressure and fracturing pressure wider,and the stronger the sealing ability of drilling fluid,the wider the gap will be.The safe drilling mud density window calculation method can analyze the relationships between collapse pressure,fracturing pressure and drilling fluid anti collapse performance,and can be used to optimize drilling fluid performance.

基于扩容强度准则的硬脆性泥岩坍塌压力计算模型

在低围压下,硬脆性泥岩在应力状态达到峰值强度前易发生扩容,当应力状态超过扩容强度后,钻井液水化作用对岩石强度的削弱增快增大,引起井壁坍塌,需制定合理的钻井液密度保持井壁稳定性。采用实验研究和理论分析相结合的方法,对硬脆性泥岩组构特征、水理性质、变形规律、强度准则和预应力后的浸泡钻井液强度变化规律进行研究,推导了基于扩容强度准则的硬脆性泥岩的井壁坍塌压力计算模型和参数计算方法,并进行了实例分析。结果表明,钻井液密度高于以峰值强度为准则计算的坍塌压力,低于以扩容强度为准则的坍塌压力,导致井周地层进入扩容状态,井周地层产生应力诱导微裂隙,激发了钻井液水化作用是井壁坍塌的根源。以扩容强度为准则确定坍塌压力,制定钻井液密度更加合理。

川西气田长水平段井壁失稳机理及对策

四川盆地川西气田中三叠统雷口坡组气藏为潮坪相沉积,埋藏深、储层薄、井壁稳定性差,前期完钻11口水平井井壁失稳频发,影响开发效益。为了确保川西气田后续长水平井打成、打好、打快,有效降低井壁失稳复杂率,以川西海相水平段为研究对象,分析其井壁失稳机理,以及裂缝渗流对井壁稳定性的影响,制定对策措施。研究结果表明:井区井壁失稳主控因素为应力、裂缝、岩性;易塌层分布在最小水平应力钻进方向、裂缝发育区,掉块岩性为石灰岩或灰质白云岩;水基钻井液条件下,岩石强度下降了11.4%~17.5%,坍塌压力增加0.11MPa/100 m;油基钻井液条件下,不考虑裂缝渗流,岩石强度不会因油基钻井液浸泡及其浸泡时间而降低,考虑裂缝渗流,裂缝摩擦系数因油基钻井液浸泡下降12.8%,坍塌压力增加0.05~0.08 MPa/100 m。结论认为,按研究成果精细预测的钻井液密度窗口、水平段轨迹优化,确保了6口长水平井顺利完钻,井壁失稳复杂率降低43%,完井测试获天然气产量172×10^(4)~325×10^(4)m^(3)/d。

海上超高温高压钻井井筒温度压力场耦合研究

为研究海上超高温高压钻井井筒温度压力的变化规律,基于流体力学和传热学理论,考虑超高温高压井筒环境对钻井液密度以及钻井液流变参数的影响,建立海上超高温高压钻井井筒温度压力耦合预测模型,并利用实例井现场随钻数据进行模型验证,分析正常钻进期间井筒温度压力的变化规律。研究结果表明:对井筒温度而言,钻井液流变性变化的影响大于钻井液密度变化的影响,耦合计算温度结果要大于不耦合计算的温度值,且两者之间的温差随井深的增加越来越大;对井筒压力而言,钻井液密度变化对当量循环密度ECD(equivalent criculating density)的影响要大于流变性对ECD的影响,且耦合计算的ECD要小于不耦合计算的ECD值。该耦合模型可以提高井筒温度压力的预测与控制精度,并降低超高温高压地层窄密度窗口中的安全钻进风险,研究结果对超高温高压钻井精准的井筒温度压力预测及控制具有重要意义。

克拉美丽气田火成岩天然裂缝漏失压力模型

克拉美丽气田火成岩地层发育裂缝,裂缝性地层中存在天然裂缝与孔隙或孔洞的复合结构,钻井过程中漏失压力与地层破裂压力差异较大。根据不同井段火成岩的裂缝—孔隙状态、裂缝开合、连通及充填情况,开展压力漏失机理研究,构建不同裂缝状态的漏失压力模型,依据地层孔隙压力、地应力等参数绘制分层漏失压力剖面,确定克拉美丽气田火成岩天然裂缝的压力漏失规律。研究表明,火成岩的闭合裂缝压力漏失受地应力控制,开启裂缝压力漏失受地层孔隙压力和充填状态影响。结合典型井的钻井参数,分析裂缝漏失压力在不同井轨迹下的变化规律,确定钻井液安全密度窗口,实现安全钻井。

高温高压小井眼水平井环空ECD综合计算模型

精确计算井筒环空ECD是钻进参数设计及安全、高效钻进的基础。为了提高其计算精度,基于高温高压下钻井液流变性测试数据,结合多元非线性回归获取钻井液密度和流变参数计算模型。通过耦合钻井液密度和流变参数回归模型与井筒传热模型,建立高温高压小井眼水平井环空ECD综合计算模型。与实测PWD数据相比,该模型平均相对误差为0.72%。研究表明,在计算高温高压小井眼水平井环空ECD时,温度和压力对钻井液密度和流变参数影响不可忽略。在钻进过程中,随着钻井液循环时间的增加,下部井段环空温度不断降低,钻井液密度与稠度系数逐渐增加,环空压耗与ECD不断增加。温度梯度和钻井液排量通过影响环空温度分布,进而影响环空ECD。地温梯度越高,环空温度越高,环空ECD越小;钻井液排量越大,环空温度越低,环空ECD越大。钻柱转速、环空尺寸和接头尺寸是影响环空ECD的重要因素。随着钻柱转速增加,环空压耗增大,进而导致环空ECD增加,但增加幅度逐渐减小;接头尺寸越大,对应的环空尺寸越小,环空压耗越大,进而导致环空ECD越大。研究结果为高温高压地层小井眼水平井的安全、高效钻进提供理论基础。

深井超深井溢流流体密度计算方法

我国油气勘探开发逐渐转向深水、深井、超深井等区域,深层地层复杂且认识不清,钻探过程中溢流漏失等事故频发,对油气勘探开发进程危害极大。处理溢流事故,优选压井方法,首先需要计算溢流流体的密度。目前,相关研究主要是通过经验法或简单的计算模型判别溢流流体的种类,该模型并未考虑温度压力的影响,存在一定误差。文章考虑了温度压力以及两相流模型的影响,基于U型管效应,建立了一种计算溢流流体密度的修正方法。该方法应用简单,经过现场验证,准确率高达95%以上,计算精度高于传统方法,溢流流体种类判别准确率高,对现场处理溢流事故、优选压井方法以及溢流后的控压钻井具有指导意义。

纳米材料改善高密度油基钻完井液沉降稳定性的研究及应用

针对现有高密度油基钻完井液在高温高压作用下流变性和沉降稳定性变差的难题,分析了高密度钻井液高温高压沉降稳定机理,研发了一种纳米乳液稳定剂,配制了两种高密度油基钻井液,分别采用OFITE高温高压流变仪和高温高压沉降稳定仪,评价了纳米乳液稳定剂对两种高密度油基钻井液高温高压作用下的流变性和沉降稳定性的影响。结果表明,浅部地层(低温低压)钻进时,压力对流变参数的影响占主导地位;在深部地层,温度对流变参数的影响大于压力的影响;通过提高油基钻井液的高温高压流变稳定性,可以改善其高温高压沉降稳定性,纳米乳液稳定剂可以明显改善高密度油基钻井液在高温高压作用下的流变稳定性和沉降稳定性。纳米乳液稳定剂改进的油基钻完井液在西南X深井的现场试验表明,钻井过程顺利,未发生因钻完井液引起的井下复杂、起下钻及测井顺畅,下套管一次到底,在近2个月的电测、等停过程中,保持了良好的高温高压流变性和沉降稳定性,为确保高温高压深井的安全钻进提供了技术保障。

低压气井泡沫压井液体系的构建及应用

伏龙泉地区气田由于长时间开发,目前已进入低产低压阶段。为保证气井稳产,需要采取修井等措施。对于低压气井,常规压井液中的固液相物质会侵入到产层,对储层形成一定的伤害,压后产能难以恢复。对泡沫发生剂、稳定剂和降滤失剂实施优选,构建密度低、漏失量小的泡沫压井液体系。结果表明:配制得到密度稳定在0.7 g/cm^(3)的低密度压井液体系,耐温120℃,体系均一,稳定时间达到24 h。现场应用能够满足生产要求,并达到储层保护的目的。